U.S. patent number 8,659,576 [Application Number 12/574,431] was granted by the patent office on 2014-02-25 for liquid crystal display with touch screen function and method for detecting external illuminance using the same.
This patent grant is currently assigned to Hydis Technologies Co., Ltd.. The grantee listed for this patent is Seong Jun An, Chang Heon Kang, Se Hwan Na, Hyun Chul Nam, Se Jong Yoo. Invention is credited to Seong Jun An, Chang Heon Kang, Se Hwan Na, Hyun Chul Nam, Se Jong Yoo.
United States Patent |
8,659,576 |
Kang , et al. |
February 25, 2014 |
Liquid crystal display with touch screen function and method for
detecting external illuminance using the same
Abstract
An Liquid Crystal Display (LCD) with a touch screen function
includes an array substrate having a display region and a
photosensitive region divided by data lines, scan lines, and common
lines, wherein the photosensitive region includes a switching
element having a first terminal connected to an (n-1).sup.th scan
line to receive a select signal and a second terminal connected to
a readout system, a charge storage element having a first terminal
connected to a third terminal of the switching element and a second
terminal connected to the common lines, and a photosensitive
element having a first terminal connected to an n.sup.th scan line
and a second terminal connected to the first terminal of the charge
storage element, wherein when the photosensitive element is turned
on according to external illuminance, the charge storage element is
discharged and the readout system detects a difference of external
illuminance.
Inventors: |
Kang; Chang Heon (Icheon-Si,
KR), An; Seong Jun (Icheon-Si, KR), Yoo; Se
Jong (Icheon-Si, KR), Nam; Hyun Chul (Icheon-Si,
KR), Na; Se Hwan (Icheon-Si, KR) |
Applicant: |
Name |
City |
State |
Country |
Type |
Kang; Chang Heon
An; Seong Jun
Yoo; Se Jong
Nam; Hyun Chul
Na; Se Hwan |
Icheon-Si
Icheon-Si
Icheon-Si
Icheon-Si
Icheon-Si |
N/A
N/A
N/A
N/A
N/A |
KR
KR
KR
KR
KR |
|
|
Assignee: |
Hydis Technologies Co., Ltd.
(Icheon-Si, KR)
|
Family
ID: |
42117017 |
Appl.
No.: |
12/574,431 |
Filed: |
October 6, 2009 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20100103130 A1 |
Apr 29, 2010 |
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Foreign Application Priority Data
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Oct 27, 2008 [KR] |
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10-2008-0105116 |
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Current U.S.
Class: |
345/175; 345/87;
178/18.09 |
Current CPC
Class: |
G06F
3/0416 (20130101); G06F 3/0412 (20130101); G02F
1/13338 (20130101); G06F 3/042 (20130101); G02F
1/13312 (20210101) |
Current International
Class: |
G06F
3/042 (20060101) |
Field of
Search: |
;345/173 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1020070082643 |
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Aug 2007 |
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KR |
|
1020070103143 |
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Oct 2007 |
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KR |
|
Primary Examiner: Harris; Dorothy
Attorney, Agent or Firm: The Webb Law Firm
Claims
What is claimed is:
1. An Liquid Crystal Display (LCD) with a touch screen function,
comprising: an array substrate having a display region and a
photosensitive region divided by data lines, scan lines, and common
lines, wherein the photosensitive region comprises: a switching
element having a first terminal connected to an (n-1).sup.th scan
line of the scan lines to receive a select signal and a second
terminal connected to a readout system; a charge storage element
having a first terminal connected to a third terminal of the
switching element and a second terminal connected to the common
lines; and a photosensitive element having a first terminal
connected to an n.sup.th scan line of the scan lines and a second
terminal connected to the first terminal of the charge storage
element, wherein when the photosensitive element is turned on
according to external illuminance, the charge storage element is
discharged and the readout system detects a difference of external
illuminance.
2. The LCD of claim 1, wherein the switching element is turned on
and the charge storage element is charged to a reference voltage of
the readout system when the (n-1).sup.th scan line is selected, the
photosensitive element is turned on and the charge storage element
is charged to a select voltage of the n.sup.th scan line when the
n.sup.th scan line is selected, and the readout system detects the
difference of external illuminance by measuring a charge amount of
the charge storage element when the (n-1).sup.th scan line is
re-selected.
3. The LCD of claim 1, wherein the switching element is turned on
and the charge storage element is charged to a reference voltage of
the readout system when the (n-1).sup.th scan line is selected, the
photosensitive element is turned on and the charge storage element
is charged to a select voltage of the n.sup.th scan line when the
n.sup.th scan line is selected, and the readout system detects the
difference of external illuminance by measuring a discharge amount
of the charge storage element when the (n-1).sup.th scan line is
re-selected.
4. The LCD of claim 1, wherein the switching element is turned on
and the charge storage element is charged to a reference voltage of
the readout system when the (n-1).sup.th scan line is selected, and
the photosensitive element is turned on and the charge storage
element is charged to a select voltage of the n.sup.th scan line
when the n.sup.th scan line is selected, and wherein when the
(n-1).sup.th scan line is re-selected, the readout system detects
the difference of external illuminance by measuring a charge amount
from the readout system to the charge storage element when a
voltage stored in the charge storage element is lower than the
reference voltage of the readout system and measuring a discharge
amount from the charge storage element to the readout system when a
voltage stored in the charge storage element is higher than the
reference voltage of the readout system.
5. The LCD of claim 2, wherein the select voltage of the scan line
is higher than the reference voltage of the readout system.
6. The LCD of claim 3, wherein the select voltage of the scan line
is higher than the reference voltage of the readout system.
7. The LCD of claim 4, wherein the select voltage of the scan line
is higher than the reference voltage of the readout system.
8. The LCD of claim 1, wherein the switching element is a
transistor in which the first terminal is a gate, the second
terminal is a source, and the third terminal is a drain.
9. The LCD of claim 1, wherein the photosensitive element is a
photodiode in which the first terminal is an anode and the second
terminal is a cathode.
10. The LCD of claim 1, wherein the photosensitive element further
comprises a third terminal connected to a scan line and is a
phototransistor in which the first terminal is a source, the second
terminal is a drain, and the third terminal is a gate.
11. A method for detecting a difference of external illuminance in
a readout system when a photosensitive element is turned on
according to the external illuminance and a charge storage element
is discharged in an LCD with a touch screen function comprising: an
array substrate having a display region and a photosensitive region
divided by data lines, scan lines, and common lines, in which a
photosensitive region comprises a switching element having a first
terminal connected to an (n-1)th scan line of the scan lines to
receive a select signal and a second terminal connected to a
readout system; a charge storage element having a first terminal
connected to a third terminal of the switching element and a second
terminal connected to the common lines; and a photosensitive
element having a first terminal connected to an nth scan line of
the scan lines and a second terminal connected to the first
terminal of the charge storage element, wherein when the
photosensitive element is turned on according to external
illuminance, the charge storage element is discharged and the
readout system detects a difference of external illuminance, the
method comprising: turning on the switching element and charging
the charge storage element to a reference voltage of the readout
system when an (n-1)th scan line of scan lines is selected; turning
on the photosensitive element and charging the charge storage
element to a select voltage of an nth scan line of the scan lines
when the nth scan line of the scan lines is selected; and
detecting, when the (n-1)th scan line of the scan lines is
re-selected in a next frame and the switching element is turned on,
the difference of external illuminance by measuring a discharge
amount from the charge storage element to the readout system if a
voltage stored in the charge storage element is higher than the
reference voltage of the readout system and measuring a charge
amount from the readout system to the charge storage element when a
voltage stored in the charge storage element is lower than the
reference voltage of the readout system.
12. The method of claim 11, wherein the select voltage of the scan
line is higher than the reference voltage of the readout
system.
13. The method of claim 11, wherein the switching element is a
transistor in which the first terminal is a gate, the second
terminal is a source, and the third terminal is a drain.
14. The method of claim 11, wherein the photosensitive element is a
photodiode in which the first terminal is an anode and the second
terminal is a cathode.
15. The method of claim 11, wherein the photosensitive element
further comprises a third terminal connected to the scan line and
is a phototransistor in which the first terminal is a source, the
second terminal is a drain, and the third terminal is a gate.
Description
BACKGROUND
1. Field of the Invention
The present invention relates to a Liquid Crystal Display (LCD)
with a touch screen function, and more particularly, to technology
for embedding a touch screen into an LCD without a separate touch
screen device.
2. Discussion of Related Art
An LCD with a touch screen function receives inputs by finger or
stylus on its surface without a separate input unit like a keypad.
The LCD with a touch screen is divided into a resistive type, a
capacitive type, a Surface Acoustic Wave (SAW) type, and an
infrared type according to a data detection method. However, since
a touch screen panel is attached to the LCD in each of these types,
thickness of a product increases, cost increases, yield decreases,
and viewing angle decreases.
To address these problems, technologies for forming a touch screen
panel inside an LCD in an in-cell type have been developed, as
disclosed in Korean Patent Application Nos. 2006-34878, 2006-15480,
etc. In U.S. Pat. Nos. 4,345,248, 5,485,177, 6,995,743, etc., which
relate to a method of using leakage current of a phototransistor,
technologies for forming both a display region and a photosensitive
region on an array substrate are disclosed.
For example, in U.S. Pat. No. 5,485,177, an array substrate
includes a display region 100 and a photosensitive region 110 as
shown in FIG. 1. Referring to FIG. 1, a photosensitive element 113,
a switching element 111, and a charge storage element 112 are
formed in the photosensitive region 110. One end of the
photosensitive element 113 is connected to the charge storage
element 112 and the other end is connected to a scan line 115. When
a voltage is applied to the scan line 115 connected to the
switching element 111, the charge storage element 112 is charged to
a voltage applied from a column line 116 of the switching element
111. Each photosensitive element 113 operates to discharge electric
charge stored in the charge storage element 112 depending on
illuminance.
However, this operation method has a disadvantage in that the load
of the scan lines is heavy since the charge storage element 112 is
connected to each scan line 115. When the resolution of the LCD
increases, a photosensitive region is not needed for each pixel. In
this case, a load difference occurs between scan lines of a pixel
with the photosensitive region and a pixel without the
photosensitive region, degrading pixel quality of the LCD.
In another example, U.S. Pat. No. 6,995,743 relates to an LCD in
which an array substrate includes a display region and a
photosensitive region. FIG. 2 is a circuit diagram of a
conventional LCD with a touch screen function, and FIG. 3 is a
cross-sectional view of the LCD.
Referring to FIG. 2, a photosensitive region 120 of the array
substrate includes a photosensitive element 122, a switching
element 123, and a charge storage element 121. In general, a
phototransistor is used as the photosensitive element 122. Gate and
source terminals of the phototransistor are connected to a common
line 125. A drain terminal of the phototransistor is connected to
the switching element 123 and one end of the charge storage element
121. The other end of the charge storage element 121 is connected
to the common line 125. Consequently, the gate and source terminals
of the phototransistor 122 are connected electrically. A gate
terminal of the switching element 123 is connected to a scan line
126. The other terminals of the switching element 123 are connected
to a readout system 127. Referring to FIG. 3, an upper portion of
the switching element 123 is covered with a black matrix 128 to
block external light, but an upper portion of the phototransistor
122 is open and exposed to external light as indicated by reference
numeral 129.
When light is incident on the photosensitive element 120, a current
flows through the phototransistor 122 and an output based on a
difference of illuminance incident on the phototransistor 122 is
read out through the switching element 123.
Here, a maximum readout voltage is proportional to a difference
between a gate-source voltage of the phototransistor 122 and a
voltage stored in the charge storage element 121 through the
switching element 123. The voltage stored in the charge storage
element 121 through the switching element 123 is set by the readout
system 127 and the gate-source voltage of the phototransistor 122
is a common voltage supplied to the common line 125 of the LCD. The
common voltage is a different value according to an LCD operation
scheme. For example, in a dot inversion scheme, the common voltage
has a value computed by subtracting an offset voltage from a middle
data voltage value when an LCD data voltage range is 0.about.10 V.
When the LCD data voltage range is -5.about.5 V, the common voltage
has a value computed by subtracting the offset voltage from 0 V
corresponding to the middle value. In a line inversion scheme, the
common voltage has a value computed by subtracting the offset
voltage from 0.about.5 V whose polarity has changed when the LCD
data voltage range is 0.about.5 V.
Consequently, in the conventional LCD with a touch screen function,
a difference between voltages applied to both ends of the charge
storage element becomes a difference between a common voltage and a
voltage applied by the readout system. Therefore, there is a
problem in that a maximum readout voltage decreases when the
difference between the voltages applied to both the ends of the
charge storage element is small.
SUMMARY OF THE INVENTION
The present invention is directed to an LCD with a touch screen
function and a method for detecting external illuminance using the
same that can reduce the load of scan lines by connecting a charge
storage element to a common line for a display operation in a
photosensitive region of an array substrate, and that can increase
a maximum readout voltage by increasing voltages applied to both
terminals of the charge storage element.
According to an aspect of the present invention, there is provided
an LCD with a touch screen function, including: an array substrate
having a display region and a photosensitive region divided by data
lines, scan lines, and common lines, wherein the photosensitive
region includes: a switching element having a first terminal
connected to an (n-1).sup.th scan line to receive a select signal
and a second terminal connected to a readout system; a charge
storage element having a first terminal connected to a third
terminal of the switching element and a second terminal connected
to the common lines; and a photosensitive element having a first
terminal connected to an n.sup.th scan line and a second terminal
connected to the first terminal of the charge storage element,
wherein when the photosensitive element is turned on according to
external illuminance, the charge storage element is discharged and
the readout system detects a difference of external
illuminance.
The switching element may be turned on and the charge storage
element may be charged to a reference voltage of the readout system
when the (n-1).sup.th scan line is selected, the photosensitive
element may be turned on and the charge storage element may be
charged to a select voltage of the n.sup.th scan line when the
n.sup.th scan line is selected, and the readout system may detect
the difference of external illuminance by measuring a charge amount
of the charge storage element when the (n-1).sup.th scan line is
re-selected.
The switching element may be turned on and the charge storage
element may be charged to a reference voltage of the readout system
when the (n-1).sup.th scan line is selected, the photosensitive
element may be turned on and the charge storage element may be
charged to a select voltage of the n.sup.th scan line when the
n.sup.th scan line is selected, and the readout system may detect
the difference of external illuminance by measuring a discharge
amount of the charge storage element when the (n-1).sup.th scan
line is re-selected.
The switching element may be turned on and the charge storage
element may be charged to a reference voltage of the readout system
when the (n-1).sup.th scan line is selected, and the photosensitive
element may be turned on and the charge storage element may be
charged to a select voltage of the n.sup.th scan line when the
n.sup.th scan line is selected. When the (n-1).sup.th scan line is
re-selected, the readout system may detect the difference of
external illuminance by measuring a charge amount from the readout
system to the charge storage element if a voltage stored in the
charge storage element is lower than the reference voltage of the
readout system and measuring a discharge amount from the charge
storage element to the readout system if a voltage stored in the
charge storage element is higher than the reference voltage of the
readout system.
The select voltage of the scan line may be higher than the
reference voltage of the readout system.
The switching element may be a transistor in which the first
terminal is a gate, the second terminal is a source, and the third
terminal is a drain.
The photosensitive element may be a photodiode in which the first
terminal is an anode and the second terminal is a cathode. The
photosensitive element may further include a third terminal
connected to a scan line and may be a phototransistor in which the
first terminal is a source, the second terminal is a drain, and the
third terminal is a gate.
According to another aspect of the present invention, there is
provided a method for detecting a difference of external
illuminance in a readout system when a photosensitive element is
turned on according to the external illuminance and a charge
storage element is discharged in an LCD with a touch screen
function in which a photosensitive region includes a switching
element, the charge storage element, and the photosensitive
element, the method including: turning on the switching element and
charging the charge storage element to a reference voltage of the
readout system when an (n-1).sup.th scan line is selected; turning
on the photosensitive element and charging the charge storage
element to a select voltage of an n.sup.th scan line when the
n.sup.th scan line is selected; and detecting, when the
(n-1).sup.th scan line is re-selected in a next frame and the
switching element is turned on, the difference of external
illuminance by measuring a discharge amount from the charge storage
element to the readout system if a voltage stored in the charge
storage element is higher than the reference voltage of the readout
system and measuring a charge amount from the readout system to the
charge storage element if a voltage stored in the charge storage
element is lower than the reference voltage of the readout
system.
The select voltage of the scan line may be higher than the
reference voltage of the readout system.
The switching element of the photosensitive region may include a
first terminal connected to a scan line and a second terminal
connected to the readout system, the charge storage element may
include a first terminal connected to a third terminal of the
switching element and a second terminal connected to a common line,
and the photosensitive element may include a first terminal
connected to a scan line and a second terminal connected to the
first terminal of the charge storage element.
The switching element may be a transistor in which the first
terminal is a gate, the second terminal is a source, and the third
terminal is a drain.
The photosensitive element may be a photodiode in which the first
terminal is an anode and the second terminal is a cathode. The
photosensitive element may further include a third terminal
connected to a scan line and may be a phototransistor in which the
first terminal is a source, the second terminal is a drain, and the
third terminal is a gate.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other objects, features and advantages of the present
invention will become more apparent to those of ordinary skill in
the art by describing in detail exemplary embodiments thereof with
reference to the accompanying drawings, in which:
FIG. 1 is a circuit diagram illustrating an example in which an
array substrate includes a display region and a photosensitive
region in a conventional LCD with a touch screen function;
FIG. 2 is a circuit diagram of a conventional LCD with a touch
screen function;
FIG. 3 is a cross-sectional view of the conventional LCD with a
touch screen function;
FIG. 4 is a conceptual diagram of an in-cell type LCD with a touch
screen function;
FIG. 5 illustrates details of operation principles of first and
second substrates of FIG. 4;
FIGS. 6A and 6B are circuit diagrams of an in-cell type LCD with a
touch screen function according to an exemplary embodiment of the
present invention;
FIG. 7 is a graph illustrating an optical current varying with
external light in a photosensitive element shown in FIGS. 6A and
6B; and
FIG. 8 is a graph illustrating operations of the circuits in the
circuit diagrams shown in FIGS. 6A and 6B.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
Exemplary embodiments of the present invention will be described in
detail below with reference to the accompanying drawings. While the
present invention is shown and described in connection with
exemplary embodiments thereof, it will be apparent to those skilled
in the art that various modifications can be made without departing
from the spirit and scope of the invention.
FIG. 4 is a conceptual diagram of an LCD with a touch screen
function and FIG. 5 illustrates details of operation principles of
first and second substrates of FIG. 4.
The present invention relates to technology for forming a touch
screen panel inside the LCD in an in-cell type. In the LCD, an
array substrate includes both a display region for a display
operation and a photosensitive region configured with a
photosensitive element, a charge storage element, and a switching
element.
Referring to FIGS. 4 and 5, the LCD includes a first substrate 200
and a second substrate 201. The second substrate 201 is formed to
face the first substrate 200 in parallel. The second substrate 201
includes a black matrix layer for covering a region where a pixel
electrode is not formed and a color filter layer for implementing
image colors. In the second substrate 201, a point spacer is
selectively formed to maintain a predetermined distance from the
first substrate 200.
The first substrate 200 includes a plurality of horizontal scan
lines formed to drive liquid crystal, a plurality of data lines
formed to intersect with the scan lines, a switching element 202
formed for data input at an intersection point between scan and
data lines, and a pixel electrode and a common electrode connected
to the switching element and formed to apply a voltage to the
liquid crystal.
FIG. 5 shows an example in which both a display region and a
photosensitive region whose characteristics varies with external
illuminance are formed on the first substrate 200 in an LCD with a
touch screen function. The photosensitive region and the display
region include switching elements 203 and 202, respectively. In the
second substrate 201, it can be seen that a portion corresponding
to the display region and a portion where a photosensitive element
is placed in the photosensitive region are not covered with a black
matrix.
As shown in FIGS. 4 and 5, external light reaches the
photosensitive region through an opening of the second substrate
201. When a human finger covers the opening of a particular
photosensitive region, the external light does not pass through a
covered portion and therefore a photosensitive element of the
photosensitive region does not operate.
FIGS. 6A and 6B are circuit diagrams of an LCD with a touch screen
function according to an exemplary embodiment of the present
invention.
Referring to FIGS. 6A and 6B, the LCD with the touch screen
function has data lines 307, scan lines 309, and a common line 308
by which a display region and a photosensitive region are divided
on an array substrate. Here, a photosensitive region 300 includes a
switching element 301, a charge storage element 302, and a
photosensitive element 303.
The switching element 301 has a gate terminal connected to a scan
line 309, a source terminal connected to a readout system 305, and
a drain terminal connected to the charge storage element 302. The
switching element 301 transfers a reference voltage supplied from
the readout system 305 to the charge storage element 302. The
switching element 301 is controlled by a select signal of the scan
line 309. The switching element 301 is configured with a Thin Film
Transistor (TFT) and a semiconductor layer of the transistor is
made of amorphous silicon (a-Si).
The charge storage element 302 has a first terminal connected to
the drain terminal of the switching element 301 and a second
terminal connected to the common line 308. The charge storage
element 302 receives and stores a reference voltage transferred
from the switching element 301 and a select voltage of the scan
line 309 transferred from the photosensitive element 303. A
capacitor can be used as the charge storage element 302.
The photosensitive element 303 is a device through which a current
flows when external light is applied. A photodiode or
phototransistor can be used as the photosensitive element 303. FIG.
6A shows an example in which the photodiode is used as the
photosensitive element 303 and FIG. 6B shows an example in which
the phototransistor is used as the photosensitive element 303.
Referring to FIG. 6A, when the photosensitive element 303 is the
photodiode, an anode terminal is connected to the scan line 309 and
a cathode terminal is connected to the first terminal of the charge
storage element 302. However, the anode terminal of the
photosensitive element is connected to the next n.sup.th scan line,
not an (n-1).sup.th scan line connected to the gate terminal of the
switching element 301, in the same photosensitive region.
Referring to FIG. 6B, when the photosensitive element 303 is the
phototransistor, its gate and source terminals connected to each
other are connected to the scan line 309, particularly, the next
n.sup.th scan line, not the (n-1).sup.th scan line connected to the
gate terminal of the switching element 301, in the same
photosensitive region. A drain terminal of the photosensitive
element 303 is connected to the first terminal of the charge
storage terminal 302 and a select voltage of the scan line 309 is
supplied to the charge storage element 302.
FIG. 7 is a graph illustrating an optical current varying with
external light in the photosensitive element. As illuminance of the
external light increases, optical current passing through the
photosensitive element increases as shown in FIG. 7.
Next, operations of the circuits in the circuit diagrams shown in
FIGS. 6A and 6B will be described with reference to FIG. 8.
First, when the (n-1).sup.th scan line 309 of FIGS. 6A and 6B is
selected, the switching element 301 is turned on and therefore the
reference voltage of the readout system 305 connected to the source
terminal of the switching element 301 is applied to node A. That
is, the charge storage element 302 is charged to the reference
voltage of the readout system 305. FIG. 8 shows an example in which
the reference voltage of the readout system is 3 V and the select
voltage of the scan line is about 15 V. At this time, it can be
seen that the voltage of node A is lower than the reference voltage
due to parasitic capacitance, etc.
Then, when the n.sup.th scan line is selected, the photosensitive
element 303 is turned on and therefore the select voltage of the
scan line 309 is applied to node A. Referring to FIG. 8, it can be
seen that node A of the charge storage element 302 is charged to
about 13 V, which is higher than the reference voltage of the
readout system when the n.sup.th scan line is selected. That is, it
can be seen that voltages conventionally applied to both terminals
of the charge storage element are as low as the reference voltage,
but voltages applied to both terminals of the charge storage
element according to the exemplary embodiment of the present
invention as shown in FIG. 8 are as high as a select voltage of the
scan line.
When external light is incident on the photosensitive region in the
LCD with the photosensitive region, a current flows through the
photosensitive element 303. When the photosensitive element 303 is
turned on according to external illuminance, charges stored in the
charge storage element 302 are leaked as a leakage current to the
scan line 309. That is, the charge storage element 302 is
discharged by a leakage current amount according to external
illuminance applied to the photosensitive element 303 before the
next (n-1).sup.th scan line is selected.
Then, when the (n-1).sup.th scan line 309 is re-selected, the
charge storage element 302 is re-charged to the reference voltage
through the switching element 301. The readout system 305 detects a
difference of external illuminance by measuring a charge amount.
When a discharge amount is small and the voltage of node A of the
charge storage element 302 is higher than the reference voltage, a
difference of external illuminance can be detected by measuring a
discharge amount from node A to the readout system 305. According
to a difference of external illuminance, a portion touched by a
finger can be distinguished from an untouched portion.
As described above, according to the present invention, a charge
storage element is connected to a common line for a display
operation in a photosensitive region, thereby it is possible to
reduce the load of scan lines and reduce a line delay when a scan
line is selected.
Conventionally, voltages applied to both terminals of the charge
storage element are as low as a reference voltage. However, the
present invention can increase a maximum readout voltage since
voltages applied to both the terminals of the charge storage
element of the photosensitive region are as high as a select
voltage of the scan line.
It will be apparent to those skilled in the art that various
modifications can be made to the above-described exemplary
embodiments of the present invention without departing from the
spirit or scope of the invention. Thus, it is intended that the
present invention covers all such modifications provided they come
within the scope of the appended claims and their equivalents.
* * * * *